The operating life of an electrolytic capacitor frequently is limited by the production of gas within the electrolyte employed in the capacitor. As a result of the formation of this gas, the equivalent series resistance (ESR) increases to an undesirable value within a comparatively short time. Thus the life of the capacitor is shortened.
It is known that production of the gas may result from a number of different mechanisms. One of these mechanisms is that formed by the thermal decomposition of the electrolyte. Another mechanism is due to the chemical reaction of the cathode, for example, aluminum with the electrolyte to produce hydrogen gas. It is also known that the electrochemical reduction of the electrolyte at the cathode produces an increase ESR in proportion to the amount of the gas produced at the cathode.
Employing nitraromatic compounds as cathode depolarizers is known to prevent this gas production. It has been found however that nitroaromatic compounds limit the operating voltages of the aluminum electrolytic capacitors and thus they are not useful depolarizers for high volt capacitors.
It has also been found that the nitroaromatic compounds are hazardous materials since they are toxic and may be absorbed through intact skin. For this additional reason, it is desirable that the nitroaromatic compounds be replaced.
Clark, U.S. Pat. No. 2,089,683, shows an electrolytic capacitor, the electrolyte of which contains a straight chain aliphatic acid containing up to 4 carbon atoms, an example in this patent is shown to be propionic acid. There is no suggestion that these acids in any way act as depolarizers.
Anderson, U.S. Pat. No. 3,539,881 shows an electrolytic capacitor in which the electrolyte employed contains monocarboxylic acid of less than 7 carbons, which acids are liquids. As examples of acids that are employed are shown propenoic, butenoic and pentenoic acids. However there is no suggestion in this patent that these acids act as depolarizers.
Belloni, U.S. Pat. No. 3,611,056 shows an electrolyte for an electrolytic capacitor containing an aliphatic polyhydroxy carboxylic acid for example citric acid. However, here too there is no suggestion that this acid functions as a depolarizer.
European Patent Application 0,246,825 shows electrolytic capacitors, the electrolytes of which contains an aliphatic carboxylic acid and shows as examples such mono-unsaturated acids as crotonic acid, acrylic acid, octenoic acid and decenoic acid. Here, too, there is no suggestion that any of the acids disclosed therein are used as depolarizers.